In Firefox:
Tools->Options->Advanced. In the Cached Web Content section, press "Clear Now".
By the way, in some other situations, if that isn't enough, you'd clear Daz cookies. Tools->Options->Privacy remove individual cookies - type "Daz" into the search box, ctrl-shift highlight the ones which are actually Daz, and hit the delete. (Mac users use that button that they have instead of the control key).

Can someone post a picture of a character riding the Steam Chopper before the Fast Grab price goes away? What I would like to see is a side view. Based on the promo pictures, I'm wondering what the feet will rest on while the chopper is in motion.